Conventional semiconductor fabrication involves the production of a number of ideally identical semiconductor devices on a silicon wafer. The process of wafer dicing is utilized to separate the discrete semiconductor devices, also known as die, from the silicon wafer. The die are subsequently prepared and placed in circuit through direct connection to a printed circuit board (“PCB”) or mounted on a substrate package that is then placed in circuit. The electrical and mechanical connection of the die to a PCB or a die to a substrate package is referred to as die-attach, also known as the level one (“L1”) interconnect. The die prepared and mounted on a substrate package is placed in circuit through direct connection of the die-attached substrate package to the PCB through the use of a conventional interconnect, for example, Pin Grid Array (“PGA”) or Ball Grid Array (“BGA”), or through the use of a connector, socket, or interposer. The electrical and mechanical connection of the die-attached substrate package to a PCB is referred to as PCB-attach, also known as the level two (“L2”) interconnect.
Die-attach is typically achieved through the use of wire-bonding or the use of flip-chip technology. In the case of wire-bonding, each die is prepared with metalized pads on the surface of the die. The metalized pads on the surface of the die are then connected to the pads of the PCB or the substrate by small wires that provide the required connectivity. The wires are typically comprised of gold, aluminum, or copper and have a diameter of micrometers (“μm”). The wires are typically connected to the pad by some combination of heat, pressure, and ultrasonic energy resulting in an electrically conductive joint.
In the case of flip-chip technology, each die is prepared with metalized pads on the surface of the die. Solder bumps, small spheres of solder, are deposited on the metalized pads of the die. The side of the die with the solder bumps is then flipped over so that the solder bumps can be mated with the substrate, or possibly a PCB. The solder bumps are then re-melted to establish an electrical and mechanical connection, typically using an ultrasound process. After re-melting the solder bumps, there is typically a small amount of space between the die and the substrate or PCB. Typically, an insulating material is flooded, through a process referred to as underfilling, between the die and the substrate or PCB.
PCB-attach is typically achieved through the use of through-hole placement or surface mount technology (“SMT”). In the case of through-hole placement, the metal pins of a package, connector, socket, or interposer are mated with corresponding metalized holes in the PCB. The through-hole package, connector, socket, or interposer is placed on the PCB such that the metal pins extend through the corresponding metalized holes in the PCB. The electrical and mechanical connection between the metal pins and the metalized holes of the PCB is typically achieved through the process of wave soldering. The semiconductor device may be placed in circuit by making the appropriate connection between the die-attached substrate through-hole package and the PCB or between the die-attached substrate package and the connector, socket, or interposer that is PCB-attached to the PCB.
In the case of SMT, a die-attached substrate package, for example a BGA package comprised, is mounted directly on corresponding metalized pads on the surface of a PCB that are covered in solder paste. The PCB is then reflowed to establish the electrical and mechanical connection between the die-attached substrate package and the metalized pads on the surface of the PCB.